I315B1-16A issues

[perette]

Hello

I'm looking for some help on trying to repair a LG 32lc46 which shows the 2 seconds to black problem.
The inverter board has been replaced once and has been working properly for some times but now here are symptoms.
Two seconds to black. Green led on as normal working.
During the two seconds a buzz sound is audible from the inverter board and seems to be located or at one of the transformer or the IC U3.
It's hard to locate it properly and sensing the vibration with my fingers does not makes me feel comfortable.

If the board is unplugged from the TV and re connected, it will buzz only after 1 seconds restart.

Caps have been changed, but no more success. I've checked and resolder each transformer and internal resistance seems to be in range of a 4018l.

The buzz sound occurs with or without ccfl tubes connected.

Any suggestion?

Best regards

Jm

[dick_barton]

Re: I315B1-16A issues

Have you any photos of your cicuit boards

[perette]

Re: I315B1-16A issues

Hi.

Here's the board.

Buzzing noise seems to come from the IC on the right or one of the transformer above.
No trace of burn anywhere.
Fuses are OK.

Best regards

Jean Marc

[budm]

Re: I315B1-16A issues

You need to trim the legs of those caps.
Are you sure the noise is not coming from the transformer?
You also need to check the resistance between the Source and Drain pin of those MOSFET's (the 8-pin devices that are for driving the transformers)

[dick_barton]

Re: I315B1-16A issues

You need to trim the excess legs of the capacitors so that they do not short against other components.
Are any of the transformers hotter than the others alongside?

Is there any sign of overheating on the underside of the circuit board especially where the transformers are mounted?

[piernov]

Re: I315B1-16A issues

https://www.badcaps.net/forum/showthread.php?t=65078

Had the same inverter. One transformer was dead, this may not be your issue but you should still check resistance of transformer windings to see if one is off.

[perette]

Re: I315B1-16A issues

Hello.

Sure I will clean the caps point.

Thanks for advices. I'll have a look at it.

I keep you posted.

Jm

[perette]

Re: I315B1-16A issues

Hello

I verified resistance of each transformater and there is only one that shows 1010 ohms instead of 1030 for all others. The one is one of my suspects for the Buzzing noise. Could such small difference explain the all behavior?

No trace of brun not heat

A newbie question. I've tried test resistance on the mosfet but did not get any reading. How to proceed?

Jean Marc

[budm]

Re: I315B1-16A issues

Can you remove the one with bozzing noise and look on the bottom side of the transformer to see if there is any sign of arcing, over heat, etc.? You can also swap its location with another transformer, also inspect the lamp connector pins, may be you are hearing high Voltage arcing.

[perette]

Re: I315B1-16A issues

Hi

So unsoldered them one by one and it ends up by moving the buzz to another transformer.
Then I resoldered them swapping their positions.

So, if it's not a transformer could if be another component on the board or even the psu?

I'm a lost

Jm

[perette]

Re: I315B1-16A issues

Hello everybody

Back on this topic.
I've recaped the psu and checked each transformer.
The problem is still there.

The inverter board gets 24v.
After switching the TV on, I get 2 seconds and then backlight turns off, but 24v is still there.
The buzz sound (with little crack) is there as soon as the inverter board switches the light on, not before.

Dead inverter board?

Best regards

Jm